Sound reproducer



5 3 1939a anon/1mm sounn REPRODUCER v F'iled July 23} 1935 mgnm;

INVENTOR W 0m M m K a Patented July 4, 1939 PATENT OFFICE SOUND REPRODUCER Glenn L. Dimmiok, Audubon, N. J., assignor to Radio Corporation of America, a corporation of Delaware Application July 23, 1935, Serial No. 32,733

4 Claims.

This invention relates to apparatus for reproducing sound from records of the push-pull type, and has for its principal object the provision of an improved sound. reproducer and method of operation whereby the relation between the response of the positive and negative half cycle tracks of the push-pull record may be easily adjusted and controlled.

In a copending application Serial No. 610,302,

filed May 9, 1932 (Docket 6738) and assigned to the same assignee as the present application, is disclosed a sound reproducer wherein light beams modulated by the positive and negative half cycle tracks of a push-pull sound record are applied to different cathodes of a photocell. To eliminate distortion in the operation of this type of reproducer it is necessary that the sensitivity or response of the diiferent cathodes be equal for the positive and negative half cycles. It is almost impossible to make photocells for different photo-- cell cathodes which have the same sensitivity. It is therefore desirable to have some means of equalizing the response of the different cells or diiierent cathodes if a single multi-cathode cell is utilized. Means have heretofore been proposed which involved equalization of the response by means of adjustment in the electrical circuits of the reproducer. In accordance with this invention, such adjustment is eifected in the optical system of the reproducer.

The invention will be better understood from the following description when considered in connection with the accompanying drawing and its scope will be pointed out in the appended 35 claims.

Referring to the drawing,

Fig. l is a diagrammatic illustration of a reproducer constructed in accordance with the invention,

Fig. 2 illustrates a detail of this apparatus, and

Fig. 3 illustrates a push-pull type of sound record on which the positive and negative half cycles of the audio current to be recorded are recorded on separate tracks.

45 The reproducer of Fig. 1 includes a lamp in from which light passes through an optical system H to a film [2 upon which the positive and negative half cycles of the audio current are recorded on separate tracks. The light modulated by these separate tracks is transmitted through a lens l3 and the parts modulated by the different tracks are transmitted respectively through lens l4 and aperture 15 to a photocell cathode l6 and through a lens I! and an aperture l8 to a photocell cathode IS. The anode of the photocell is indicated at 20. From the photocell current is supplied to the primary of a transformer 2| which is connected in a well known manner to the input circuit of an amplifier. Further details of the record l2 are shown 5 in Fig. 3. As will be readily understood, the light modulated by the sound track A is projected on the cathode it, that modulated by the sound track B is projected on the cathode l9 and the resulting sound modulated currents are com- 10 bined in the primary winding of the transformer 2|.

It is necessary that the currents reproduced when the component tracks of the push-pull record be properly balanced with respect to one 15 another. Such a balance is not easily realized for the reason that the cathodes of a single or different cells do not ordinarily have the same response or sensitivity. To eliminate unbalance or distortion it is obviously necessary that the response of the two photo-electric elements be equalized. In the reproducer of Fig. 3 this result is achieved by means of a shutter device interposed in the optical system. As shown more clearly in Fig. 2, this shutter includes a membe 22 provided with apertures i5 and i3 and a par of shutters 23 and 2d mounted on a member pivoted at 25 and adjustable by means of a handle 26. It will be apparent that these shutters may be readily adjusted so as to maintan any desired relation between the illuminaiion of the cathodes i6 and i9.

In the present state of the art it is sometimes desirable to adapt a reproducer to the use of either a push-pull or single sound record. This adaptation is readily accomplished by adjusting the shutters 23 and 24 so that one of the apertures H3 or I8 is completely covered and the other is completely uncovered. Under this condition, the reproducer operates to reproduce a 6 single sound track on which are recorded both the positive and negative half cycles.

It Will be understood that the shutter device does not have to be located adjaccnt the photocell as indicated in Fig. l but may be interposed in the light beam at other points such, for example, as the plane of the lenses M and II. It is desirable, of course, that the direction of the motion of the shutters be at right angles to the direction of the vibration of the Waves on the film. Another Way of obtaining optical equalization would be the use of an optical wedge instead of the shutter. In this arrangement the two wedges would be so positioned in any instance that their transmission would be inversely proportional to the corresponding photocell sensitivity. Also the two half cycle tracks could be illuminated by separate light sources and the brightness of the two sources could be independently regulated to equalize the sensitivity or" the two cells.

I claim:

1. In an apparatus for reproducing a pushpull sound record having its positive and negative half cycles recorded on complementary tracks spaced from one another, the combination of means for modulating a plurality of light each in accordance with a difierent one of said tracks, a plurality of complementary photo-electric elements connected in push-pull and each responsive to a different one of said modulated beams, and means for adjusting the relation between the illumination of said elements for balancing the output thereof.

2. In an apparatus for reproducing a pushpull sound record having its positive and negative half cycles recorded on complementary tracks spaced from one another, the combination of means for modulating a plurality of light beams each in accordance with a different one of said tracks, a plurality of complementary photo-electric elements connected in push-pull and each responsive to a different one of said modulated beams, means for adjusting the relation between the illumination of said elements for balancing the output thereof, and means for combining the output of said elements.

3. In an apparatus for reproducing a sound record having different components recorded on complementary tracks spaced from one another, the combination of means for modulating a plurality of light beams each in accordance with a different one of said tracks, a plurality of photoelectric elements each responsive to a different one of said modulated beams, and means operable to obscure one or the other of said beams and to adjust the relation between the illumination of said elements.

4. In an apparatus for reproducing a sound record having different components recorded on complementary tracks spaced from one another, the combination of means for modulating a plurality of light beams each in accordance with a difierent one of said tracks, a plurality of photoelectric elements connected in push-pull and each responsive to a different one of said modulated beams, and means including a plurality of shutters operable to adjust the relation between the illumination of said elements for balancing the output thereof.

GLENN L. DIMMICK. 

